1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) used in optical displays, and more particularly to an LCD to be used in temporary storage devices such as television and computer screens, large-screen displays, timepieces, electronic calculators, soft-printing screens, etc., and the method of manufacturing the LCD.
2. Description of the Related Art
One type of current LCD uses a simple X-Y matrix or thin-film transistor driving method, both of which use twisted nematic (TN) or super twisted nematic (STN) liquid crystal. A polarizer must be used with the TN or STN liquid crystal. Polarizers used with the LCDs absorb over 50% of the incident light. Therefore, the LCDs in a display with a polarizer must generate over 50% more light than LCDs in a display without a polarizer for both LCDs to supply the same amount of light to a user. Consequently, a display using current LCDs consumes a lot of power to produce sufficient light to a user.
The structure of LCDs using the X-Y matrix or thin-film transistor driving methods is generally sealed by interposing liquid crystal between two glass plates. An overall uniform cell gap between the glass plates is necessary. Enlargement of such an LCD is difficult due to the limited precision of plate glass manufacturing.
Accordingly, a technique must be developed to form an LCD without a polarizer on a single substrate using a pattern forming technique, in order to increase the efficiency of the light emitted from the LCD. Such an LCD would have better contrast and allow enlargement of the LCD.
Examples of LCDs without a polarizer include a cholesteric nematic transition (CNT) type (which uses a phase transition effect) and a dynamic scattering mode (DSM) type liquid crystal. Liquid crystal is sealed between two glass plates in the CNT type LCD. The DSM type LCD has a slow response time and cannot be thinly formed so it is no longer commonly used.
An example of an LCD formed on one substrate is a polymer-dispersed liquid crystal (PDLC) type. The PDLC type LCD is arranged more densely due to the single substrate formation. In order to obtain a picture having a desired contrast ratio, the PDLC is made of a polymer material more than half of whose volume is light-transmitting. Scattered light is used to form characters or objects observed by a user. However, sufficient light scattering by the liquid crystal layer must be induced to ensure enough scattering of light for the user to notice the scattered and reflected light (i.e. the displayed characters). The shielding of rearwardly incident light must be enhanced also. To attain these requirements, the thickness of the liquid crystal layer should be at least 20 .mu.m which makes its response time very slow (more than 1 ems).
Still other examples include an LCD for multi-purpose usage in which glass plates are inserted between liquid crystal layers. The objective of the multi-purpose LCD is not to improve the efficiency or contrast of light use. There is a two-story type STN display for compensating polarization, but it is only a background color compensator (using the interference of light).
Even though paper white displays are available, it has not yet been recognized that in a conventional LCD, a large amount of LCD layer front-scattering (transmission) greatly diminishes contrast (specifically, faint whiteness). Thus, LCD's have, in the past, used light with poor efficiency.